Page 36 - REMOVABLE ORTHODONTIC APPLIANCES

28 Removable Orthodontic Appliances
produce localized tooth movement. They can
also be used, as described below, to provide
intermaxillary traction.
To align a displaced tooth, a point of attach-
ment needs to be bonded to the tooth - usually
a stainless steel hook or button. An elastic can
then be engaged between the appliance and the
displaced tooth. Elastics need to be changed by
Figure 3.28 A double guide pin screw, (a) Closed,
(b) Open. the patient on a regular basis and care must be
used not to exceed the appropriate force limits.
Elastics have been used in an attempt to reduce
an overjet, but this is generally considered to be
delayed. Screws apply intermittenl large an unsatisfactory method and is not recom-
forces, which decrease as tooth movement mended.
occurs. The large force is acceptable only
because the activation at any one time is small
(less than 0.2 mm). The tooth is thus moved Intermaxillary traction
within the limits of the periodontal ligament
and extensive hyalinization will not be A removable appliance may be fitted in the
produced. Spring-loaded screws are available, opposing arch to a fixed appliance, to allow
in which a spring within the screw dissipates the use of intermaxillary elastics. This is
the force over a period of time. Although particularly useful when there is a well-
these offer theoretical advantages, they are aligned lower arch, which does not require
bulkier, more expensive and seem to offer few any active tooth movement. A well fitting
clinical advantages. removable appliance can provide an anchor-
age point for either class II or class III elastic
traction. The use of elastic intermaxillary
Adjustment
traction with removable appliances alone is
The patient is given the key to adjust the screw. not satisfactory.
It is worthwhile incorporating a marker in the
baseplate to indicate the direction in which the
screw is to be turned. An adjustment of one Localized tooth movement
quarter-turn each week will produce a rate of
tooth movement of about 1 mm per month. The Intraoral elastics can be used to move a single
patient must ensure that the appliance seats tooth. A hook, bonded on to the surface of the
home fully after adjustment. In some situations tooth provides a point of attachment for the
it is possible to adjust the screw twice weekly, elastic, which also engages an appropriately
but this may lead to anchorage loss and the placed hook on the appliance.
appliance may not seat home fully, so that Occlusal movement of partially erupted
retention is less good. It is possible to monitor teeth can be satisfactorily achieved by this
the expansion achieved by the use of holes method and the palatal acrylic of the appliance
drilled into the acrylic in each half of appliance provides anchorage for the movement.
and to measure with dividers at each visit. Buccally placed canines that are crowded
Alternatively the screw may be turned back at and partially erupted can also be retracted in
each visit and the number of turns recorded in this manner. The hook can be bonded on to
the notes. the buccal surface of the tooth. The removable
appliance carries a buccal arm with a hook at
the end of the arm, which is positioned so that
it is possible to apply an occlusally directed
Elastics force on the tooth. The patient has to engage
the elastic when fitting the appliance and a
Elastics may be used intraorally with remov- certain degree of manual dexterity is neces-
able appliances and may be particularly useful sary. Teeth that are erupting palatally are
in conjunction with a bonded attachment to considerably more difficult for a patient to